<template>
  <div class="pagination">
    <!-- 如果当前页是1就禁止点击  :disabled="pageNo == 1" -->
    <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo-1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" 
      @click="$emit('getPageNo', 1)"
      :class="{active:pageNo ==1}">1
    </button>
    <button v-if="startNumAndEndNum.start > 2">...</button>
    
    <!-- 中间部分    错误是因为 v-for 和 v-if 不能一起写-->
    <button v-for="(page, index) in startNumAndEndNum.end" :key="index" 
     v-if="page>= startNumAndEndNum.start" 
      @click="$emit('getPageNo', page)" 
      :class="{active: pageNo == page}">{{page}}
    </button>
    
    <!-- 下 -->
    <button v-if="startNumAndEndNum.end < totalPage -1">...</button>
    <button v-if="startNumAndEndNum.end < totalPage"
     @click="$emit('getPageNo',totalPage)"
     :class="{active: pageNo==totalPage}"><!-- 当前页等于总数就有颜色 -->
     {{totalPage}}
    </button>
    <button :disabled="pageNo==totalPage" @click="$emit('getPageNo', pageNo + 1)">下一页</button>   

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  // pageNo当前第几页,pageSize每页有几条数据,total总共有几条数据(数组),continues连续页码数
  props:['pageNo','pageSize','total','continues'],
  computed:{
    //总共多少页
    totalPage(){
      //向上取整
      return Math.ceil(this.total/this.pageSize);
    },
    //计算出连续的页码的起始数字与结束数字【连续页码的数字：至少是5】
    startNumAndEndNum(){
      const { continues, pageNo, pageSize} = this;
      //先定义两个变量存储起始数字与结束数字
      let start = 0, end = 0;
      //连续页码数字5 【就是至少5页】，如果出现不正常的现象【就是不够五页】
      //不正常现象【总页数没有连续页码多】
      if(continues > this.totalPage){
        start = 1;
        end = this.totalPage;
      }else{
        //正常现象【连续页码5，但是你的总页数一定是大于5 】
        //起始数字
        start = pageNo - parseInt(continues / 2);
        //结束数字
        end = pageNo + parseInt(continues / 2);
        //把出现不正常的现象【start数字出现 0 | 负数】纠正
        if(start < 1){
          start = 1;
          end = continues;
        }
       //把出现不正常的现象【end数字大于总页数】纠正
       if(end > this.totalPage){
        end = this.totalPage;
        start = this.totalPage - continues + 1;
       }
      }
      return {start, end}
    }
  }
};
</script>

<style lang="less" scoped>
.pagination {
    text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }
    &.active {
      cursor: not-allowed;
      background-color: pink;
      color: #fff;
    }
  }
}

</style>